1. Field of the Invention
The present invention relates to a navigation system.
2. Description of the Related Art
A navigation apparatus installed in a vehicle such as a car is known to use a position detection apparatus called a GPS (Global Positioning System) and/or other sensors whereby information is provided to a driver, which information typically includes the current position of the vehicle and a route to a destination displayed on a screen.
Such a navigation apparatus is known to warn a driver when the vehicle is approaching a location, such as a curve, where safety is difficult to predict. A warning that the vehicle is approaching such a curve is given by a warning sound, by a change in the color of a road displayed on a map screen of a display, or by display of a warning symbol (as disclosed, for example, in Japanese Unexamined Patent Application Publication No. 9-35186 or Japanese Unexamined Patent Application Publication No. 9-189565).
However, the conventional navigation apparatus does not have the capability of providing appropriate information to a driver for travel on a difficult road, such as a mountain road which has a plurality of successive curves, changes in gradient, and/or poor visibility. When a road includes many successive curves, if a similar warning is displayed for all curves, the driver cannot distinguish a tight curve from a gentle (slight) curve, and the driver may be preoccupied with a warning for a slight curve, causing the driver to miss a warning for a tight curve. That is, important information may become lost in a relatively greater quantity of less important information.
When a vehicle runs on a difficult road such as a mountain road or the like, a driver needs to make various decisions, one after another, within a short time, relating, for example, to curvature, change in gradient, approach of another vehicle, etc., and thus the driver needs to concentrate all his/her energy on driving. Repeated pressing of the brake pedal, over/under steering, and/or other inappropriate driving operations can cause the vehicle to become unstable.